Vagus nerve stimulation attenuates cerebral ischemia and reperfusion injury via endogenous cholinergic pathway in rat

Vagus Nerve Stimulation Attenuates Cerebral Microinfarct and Colitis-induced Cerebral Microinfarct Aggravation in Mice

Cerebral cortical microinfarct (CMI) is common in patients with dementia and cognitive decline. Emerging studies reported that intestinal dysfunction influenced the outcome of ischemic stroke and that vagus nerve stimulation (VNS) protected against ischemic stroke. However, the effects of intestinal dysfunction and VNS on CMI are not clear. Therefore, we examined the influence of colitis and VNS on CMI and the mechanisms of VNS attenuating CMI in mice with colitis. CMI was induced using a two-photon laser. Colitis was induced using oral dextran sodium sulfate (DSS). The cervical vagus nerve was stimulated using a constant current. In vivo blood-brain barrier (BBB) permeability was evaluated using two-photon imaging. Infarct volume, microglial and astrocyte activation, oxidative stress and proinflammatory cytokine levels were assessed using immunofluorescent and immunohistochemical staining. The BBB permeability, infarct volume, activation of microglia and astrocytes and oxidative stress increased significantly in mice with colitis and CMI compared to those in mice with CMI. However, these processes were reduced in CMI mice when VNS was performed. Brain lesions in mice with colitis and CMI were significantly ameliorated when VNS was performed during the acute phase of colitis. Our study demonstrated that VNS alleviated CMI and this neuroprotection was associated with the suppression of BBB permeability, neuroinflammation and oxidative stress. Also, our results indicated that VNS reduced colitis-induced microstroke aggravation.

Inflammation in stroke: the role of cholinergic, purinergic and glutamatergic signaling

The inflammatory response is a major factor in stroke pathophysiology and contributes to secondary neuronal damage in both acute and chronic stages of the ischemic injury. Recent work in experimental cerebral ischemia has demonstrated the involvement of neurotransmitter signaling in the modulation of neuroinflammation. The present review discusses recent findings on the therapeutic potential and diagnostic perspectives of cholinergic, purinergic and glutamatergic receptors and transporters in experimental stroke. It provides evidence of the role of neurotransmission signaling as a promising inflammatory biomarker in stroke. Finally, recent molecular imaging studies using positron emission tomography of cholinergic receptors and glutamatergic transporters are outlined along with their potential as novel anti-inflammatory therapy to reduce the outcome of cerebral ischemia.

Sub-acute administration of lower doses of nicotine caused sex-dependent improvement of renal function in Wistar rats

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Exposure to nicotine is associated with sex-dependent variation in electrolyte disturbances.

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Lower doses of sub-acute nicotine administration enhanced renal function.

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Nicotine-enhanced renal function is more pronounced in female than in male Wistar rats.

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Nicotine-enhanced renal function may be mediated through α7-nAchR.

The adverse and beneficial health effects of nicotine (NIC), the major alkaloid found in cigarettes and tobacco, are controversial. Most studies on NIC have focused on its effects on cardiovascular and nervous functions. This study aimed at determining dose- and sex-specific effects of sub-acute (28 days) NIC administration on some indices of kidney function in Wistar rats. Forty rats (20 males and 20 females), 8–9 weeks old (each housed in separate metabolic cage), were used for this study such that graded doses of NIC (1, 2 and 4 mg/kg i.p. for 28 days) were administered to both sexes while each control received distilled water at 0.2 mL/100 g i.p. Blood was collected under ketamine anesthesia (10 mg/kg i.m) for analyses and results obtained were compared at p < 0.05. The result showed beneficial alterations in plasma and urine level of creatinine, urea and uric acid (p < 0.05) as well as plasma and urine electrolyte level (Na⁺ and K⁺) in both sexes (p < 0.05). Also, there was significant improvement in creatinine clearance (p < 0.05) with no appreciable difference in their histological examination. Although these beneficial effects were more pronounced in the female than in the male (p < 0.05), administration at the highest dose showed potentially deleterious alterations from normal beneficial trend (p < 0.05) in both sexes. It was concluded that sub-acute administration of lower doses of NIC improves kidney function of Wistar rats; an effect that was more pronounced in the females than their male counterparts.

Electroacupuncture brain protection during ischemic stroke: A role for the parasympathetic nervous system

The demand for using parasympathetic activation for stroke therapy is unmet. In the current study, we investigated whether the neuroprotection provided by electroacupuncture (EA) in an experimental stroke model was associated with activation of the parasympathetic nervous system (PNS). The results showed that parasympathetic dysfunction (PD), performed as unilateral vagotomy combined with peripheral atropine, attenuated both the functional benefits of EA and its effects in improving cerebral perfusion, reducing infarct volume, and hindering apoptosis, neuronal and peripheral inflammation, and oxidative stress. Most importantly, EA rats showed a dramatically less reduction in the mRNA level of choline acetyltransferase, five subtypes of muscarinic receptors and α7nAChR, suggesting the inhibition of the impairment of the central cholinergic system; EA also activated dorsal motor nucleus of the vagus, the largest source of parasympathetic pre-ganglionic neurons in the lower brainstem (detected by c-fos immunohistochemistry), and PD suppressed these changes. These findings indicated EA may serve as an alternative modality of PNS activation for stroke therapy.

Baroreflex stimulation attenuates central but not peripheral inflammation in conscious endotoxemic rats

We previously reported that activation of the baroreflex, a critical physiological mechanism controlling cardiovascular homeostasis, through electrical stimulation of the aortic depressor nerve attenuates joint inflammation in experimental arthritis. However, it is unknown whether baroreflex activation can control systemic inflammation. Here, we investigate whether baroreflex activation controls systemic inflammation in conscious endotoxemic rats. Animals underwent sham or electrical aortic depressor nerve stimulation initiated 10 min prior to a lipopolysaccharide (LPS) challenge, while inflammatory cytokine levels were measured in the blood, spleen, heart and hypothalamus 90 min after LPS treatment. Baroreflex activation did not affect LPS-induced levels of pro-inflammatory (tumor necrosis factor, interleukin 1β and interleukin 6) or anti-inflammatory (interleukin 10) cytokines in the periphery (heart, spleen and blood). However, baroreflex stimulation attenuated LPS-induced levels of all these cytokines in the hypothalamus. Notably, these results indicate that the central anti-inflammatory mechanism induced by baroreflex stimulation is independent of cardiovascular alterations, since aortic depressor nerve stimulation that failed to induce hemodynamic changes was also efficient at inhibiting inflammatory cytokines in the hypothalamus. Thus, aortic depressor nerve stimulation might represent a novel therapeutic strategy for neuroprotection, modulating inflammation in the central nervous system.

Acupuncture and neuroregeneration in ischemic stroke

Acupuncture is potentially beneficial for post-stroke rehabilitation and is considered a promising preventive strategy for stroke. Electroacupuncture pretreatment or treatment after ischemic stroke by using appropriate electroacupuncture parameters generates neuroprotective and neuroregenerative effects that increase cerebral blood flow, regulate oxidative stress, attenuate glutamate excitotoxicity, maintain blood-brain barrier integrity, inhibit apoptosis, increase growth factor production, and induce cerebral ischemic tolerance.

Nicotinic Acetylcholine Receptor Alpha7 Subunit Mediates Vagus Nerve Stimulation-Induced Neuroprotection in Acute Permanent Cerebral Ischemia by a7nAchR/JAK2 Pathway

Background

The role of nicotinic acetylcholine receptor alpha7 subunit (a7nAchR) in the treatment of acute cerebral ischemia by VNS has not been thoroughly clarified to date. Therefore, this study aimed to investigate the specific role of a7nAchR and explore whether this process is involved in the mechanisms of VNS-induced neuroprotection in rats undergoing permanent middle cerebral artery occlusion (PMCAO) surgery.

Material/Methods

Rats received a7nAChR antagonist (A) or antagonist placebo injection for control (AC), followed by PMCAO and VNS treatment, whereas the a7nAChR agonist (P) was utilized singly without VNS treatment but only with PMCAO pretreatment. The rats were randomly divided into 6 groups: sham PMCAO, PMCAO, PMCAO+VNS, PMCAO+VNS+A, PMCAO+VNS+AC, and PMCAO+P. Neurological function and cerebral infarct volume were measured to evaluate the level of brain injury at 24 h after PMCAO or PMCAO-sham. Moreover, the related proteins levels of a7nAChR, p-JAK2, and p-STAT3 in the ischemic penumbra were assessed by Western blot analysis.

Results

Rats pretreated with VNS had significantly improved neurological function and reduced cerebral infarct volume after PMCAO injury (p<0.05). In addition, VNS enhanced the levels of a7nAchR, p-JAK2, and p-STAT3 in the ischemic penumbra (p<0.05). However, inhibition of a7nAchR not only attenuated the beneficial neuroprotective effects induced by VNS, but also decreased levels of p-JAK2 and p-STAT3. Strikingly, pharmacological activation of a7nAchR can partially substitute for VNS-induced beneficial neurological protection.

Conclusions

These results suggest that a7nAchR is a pivotal mediator of VNS-induced neuroprotective effects on PMCAO injury, which may be related to suppressed inflammation via activation of the a7nAchR/JAK2 anti-inflammatory pathway.

Activation of the cholinergic anti-inflammatory pathway by GTS-21 attenuates cisplatin-induced acute kidney injury in mice

Acute kidney injury (AKI) is the most common side effect of cisplatin, a widely used chemotherapy drug. Although AKI occurs in up to one third of cancer patients receiving cisplatin, effective renal protective strategies are lacking. Cisplatin targets renal proximal tubular epithelial cells leading to inflammation, reactive oxygen species, tubular cell injury, and eventually cell death. The cholinergic anti-inflammatory pathway is a vagus nerve-mediated reflex that suppresses inflammation via α7 nicotinic acetylcholine receptors (α7nAChRs). Our previous studies demonstrated the renoprotective and anti-inflammatory effects of cholinergic agonists, including GTS-21. Therefore, we examined the effect of GTS-21 on cisplatin-induced AKI. Male C57BL/6 mice received either saline or GTS-21 (4mg/kg, i.p.) twice daily for 4 days before cisplatin and treatment continued through euthanasia; 3 days post-cisplatin mice were euthanized and analyzed for markers of renal injury. GTS-21 significantly reduced cisplatin-induced renal dysfunction and injury (p<0.05). GTS-21 significantly attenuated renal Ptgs2/COX-2 mRNA and IL-6, IL-1β, and CXCL1 protein expression, as well as neutrophil infiltration after cisplatin. GTS-21 blunted cisplatin-induced renal ERK1/2 activation, as well as renal ATP depletion and apoptosis (p<0.05). GTS-21 suppressed the expression of CTR1, a cisplatin influx transporter and enhanced the expression of cisplatin efflux transporters MRP2, MRP4, and MRP6 (p<0.05). Using breast, colon, and lung cancer cell lines we showed that GTS-21 did not inhibit cisplatin’s tumor cell killing activity. GTS-21 protects against cisplatin-AKI by attenuating renal inflammation, ATP depletion and apoptosis, as well as by decreasing renal cisplatin influx and increasing efflux, without impairing cisplatin-mediated tumor cell killing. Our results support further exploring the cholinergic anti-inflammatory pathway for preventing cisplatin-induced AKI.

Hereditary angioedema: Assessing the hypothesis for underlying autonomic dysfunction

Background

Attacks of Hereditary Angioedema due to C1-inhibitor deficiency (C1-INH-HAE)are often triggered by stressful events/hormonal changes.

Objective

Our study evaluates the relationship between autonomic nervous system (ANS) and contact/complement system activation.

Methods

Twenty-three HAE patients (6 males, mean age 47.5±11.4 years) during remission and 24 healthy controls (8 males, mean age 45.3±10.6 years) were studied. ECG, beat-by-beat blood pressure, respiratory activity were continuously recorded during rest (10’) and 75-degrees-head-up tilt (10’). C1-INH, C4, cleaved high molecular weight kininogen (cHK) were assessed; in 16 patients and 11 controls plasma catecholamines were also evaluated. Spectral analysis of heart rate variability allowed extraction of low-(LF) and high-(HF) frequency components, markers of sympathetic and vagal modulation respectively.

Results

HAE patients showed higher mean systolic arterial pressure (SAP) than controls during both rest and tilt. Tilt induced a significant increase in SAP and its variability only in controls. Although sympathetic modulation (LFnu) increased significantly with tilt in both groups, LF/HF ratio, index of sympathovagal balance, increased significantly only in controls.

At rest HAE patients showed higher noradrenaline values (301.4±132.9 pg/ml vs 210.5±89.6pg/ml, p = 0.05). Moreover, in patients tilt was associated with a significant increase in cHK, marker of contact system activation (49.5 ± 7.5% after T vs 47.1 ± 7.8% at R, p = 0.01).

Conclusions

Our data are consistent with altered ANS modulation in HAE patients, i.e. increased sympathetic activation at rest and blunted response to orthostatic challenge. Tilt test-induced increased HK cleavage suggests a link between stress and bradykinin production.

α7 nicotinic acetylcholine receptor agonist attenuates the cerebral injury in a rat model of cardiopulmonary bypass by activating the Akt/GSK3β pathway

α7 nicotinic acetylcholine receptor (α7nAchR) agonist treatment may provide a promising therapeutic effect for cerebral injuries. However, it is unclear whether the activation of α7nAchR agonist may reduce cerebral injuries induced by cardiopulmonary bypass (CPB). A total of 96 male Sprague‑Dawley rats were randomly divided into four groups (n=24/group): i) Sham operation group; ii) CPB group; iii) CPB + α7nAchR agonist group; and iv) CPB + α7nAchR agonist + α7nAchR antagonist group. Following treatment, 24 rats from each group were sacrificed and the serum and hippocampal tissues were collected. The serum expression levels of S100β, interleukin 6 and tumor necrosis factor α were evaluated by ELISA, hippocampal tissues were analyzed by histopathological examination using hematoxylin & eosin and terminal deoxynucleotidyl‑transferase‑mediated dUTP nick‑end labeling (TUNEL) staining and Caspase 3 expression in the hippocampal tissues was evaluated by immunohistochemistry. In addition, Caspase 3, Akt and glycogen synthase kinase 3β (GSK3β), as well as phosphorylated (p)‑Akt and (p)‑GSK3β were examined by western blot assay. The present study demonstrated that α7nAchR agonist treatment was able to alleviate pathological damage and inhibit hippocampal cell apoptosis and inflammatory response. α7nAchR agonist treatment also increased the expression levels of p‑Akt and p‑GSK3β, which indicated an upregulation in Akt/GSK3β signaling. These data suggested that α7nAchR agonist may provide a promising new therapeutic approach for cerebral injury caused by CPB.

Vagus Nerve Attenuates Hepatocyte Apoptosis upon Ischemia-Reperfusion via α7 Nicotinic Acetylcholine Receptor on Kupffer Cells in Mice

BACKGROUND

Hepatic ischemia-reperfusion (HIR) injury is a complication of liver surgery. As much as 50% of hepatocytes undergo apoptosis within the first 24 h of reperfusion. The neurotransmitters of the vagus nerve can activate α7 nicotinic acetylcholine receptor (α7nAChR) on macrophages. The function of Kupffer cells (KCs) determines HIR injury. We hypothesize that the vagus nerve could attenuate HIR-induced hepatocyte apoptosis by activating α7nAChR on KCs.

METHODS

Hepatic vagotomized C57BL/6J mice, KC-eliminated C57BL/6J mice, and α7nAChR mice were used for HIR. Primary KCs and hepatocytes were subjected to hypoxia/reoxygenation (HR). Liver injury, hepatocyte apoptosis, reactive oxygen species (ROS) production, and soluble CD163 were measured.

RESULTS

Hepatic vagotomy and α7nAChR caused higher levels of alanine transaminase and liver caspase-3 and -8 activity by HIR. Activating α7nAChR attenuated these changes in wild-type but not in the α7nAChR mice. Furthermore, activating α7nAChR diminished hepatic injury and reduced liver apoptosis by HIR in vagotomized mice. In vitro, activating α7nAChR reduced apoptosis of hepatocytes cocultured with KCs that suffered HR. Similar to the effects by catalase, activating α7nAChR on KCs reduced ROS and H2O2 by HR. The supernatant from KCs, with α7nAChR activated or catalase treated, prevented hepatocyte apoptosis by HR. Finally, KC elimination reduced HIR-induced H2O2 production in mice. Activating α7nAChR significantly attenuated soluble CD163 both in mice by HIR (serum: 240 ± 34 vs. 446 ± 72; mean ± SD; n = 8; P < 0.01) and in KCs by HR (supernatant: 4.23 ± 0.06 vs. 5.60 ± 0.18; n = 3; P < 0.01).

CONCLUSIONS

The vagus nerve could minimize HIR-induced liver apoptosis through activating α7nAChR on KCs possibly by preventing their excessive ROS production.

C1 neurons mediate a stress-induced anti-inflammatory reflex in mice

C1 neurons (C1), located in the medulla oblongata, mediate adaptive autonomic responses to physical stressors (e.g. hypotension, hemorrhage, lipopolysaccharide). We describe here a powerful effect of restraint stress mediated by C1: protection against renal ischemia-reperfusion injury (IRI).

Restraint stress or optogenetic C1 stimulation (10 min) protected mice from IRI. The protection was reproduced by injecting splenic T-cells pre-incubated with noradrenaline or splenocytes harvested from stressed mice. Stress-induced IRI protection was absent in α7nAChR^−/− mice and greatly reduced by destroying or transiently inhibiting C1. The protection conferred by C1 stimulation was eliminated by splenectomy, ganglionic blocker administration, or β₂-adrenergic receptor blockade. Although C1 stimulation elevated plasma corticosterone and increased both vagal and sympathetic nerve activity, C1-mediated IRI protection persisted after subdiaphragmatic vagotomy or corticosterone receptor blockade.

In conclusion, acute stress attenuates IRI by activating a cholinergic, predominantly sympathetic, anti-inflammatory pathway. C1 neurons are necessary and sufficient to mediate this effect.

Vagus nerve stimulation inhibits cortical spreading depression

Vagus nerve stimulation has recently been reported to improve symptoms of migraine. Cortical spreading depression is the electrophysiological event underlying migraine aura and is a trigger for headache. We tested whether vagus nerve stimulation inhibits cortical spreading depression to explain its antimigraine effect. Unilateral vagus nerve stimulation was delivered either noninvasively through the skin or directly by electrodes placed around the nerve. Systemic physiology was monitored throughout the study. Both noninvasive transcutaneous and invasive direct vagus nerve stimulations significantly suppressed spreading depression susceptibility in the occipital cortex in rats. The electrical stimulation threshold to evoke a spreading depression was elevated by more than 2-fold, the frequency of spreading depressions during continuous topical 1 M KCl was reduced by ∼40%, and propagation speed of spreading depression was reduced by ∼15%. This effect developed within 30 minutes after vagus nerve stimulation and persisted for more than 3 hours. Noninvasive transcutaneous vagus nerve stimulation was as efficacious as direct invasive vagus nerve stimulation, and the efficacy did not differ between the ipsilateral and contralateral hemispheres. Our findings provide a potential mechanism by which vagus nerve stimulation may be efficacious in migraine and suggest that susceptibility to spreading depression is a suitable platform to optimize its efficacy.

L-PGDS Mediates Vagus Nerve Stimulation-Induced Neuroprotection in a Rat Model of Ischemic Stroke by Suppressing the Apoptotic Response

The role of lipocalin prostaglandin D2 synthase (L-PGDS) in brain ischemia has not been fully clarified to date. Vagus nerve stimulation (VNS) protects against cerebral ischemia/reperfusion (I/R) injury, but the mechanisms involved need further exploration. This study investigated the role of L-PGDS in cerebral I/R and whether this process was involved in the mechanism of VNS-mediated neuroprotection. Male Sprague-Dawley rats were pretreated with a lentiviral vector (LV) through intracerebroventricular injection, followed by middle cerebral artery occlusion (MCAO) and VNS treatment. The expression of L-PGDS in the peri-infarct cortex was examined. The localization of L-PGDS was determined using double immunofluorescence staining. Neurologic scores, infarct volume and neuronal apoptosis were evaluated at 24 h after reperfusion. The expression of apoptosis-related molecules was measured by western blot analysis. The expression of L-PGDS in the peri-infarct cortex increased at 12 h, reached a peak at 24 h after reperfusion, and lasted up to 3 days. VNS treatment further enhanced the expression of L-PGDS following ischemic stroke. L-PGDS was mainly expressed in neurons in the peri-infarct cortex. I/R rats treated with VNS showed better neurological deficit scores, reduced infarct volume, and decreased neuronal apoptosis as indicated by the decreased levels of Bax and cleaved caspase-3 as well as increased levels of Bcl-2. Strikingly, the beneficial effects of VNS were weakened after L-PGDS down-regulation. In general, our results suggest that L-PGDS is a potential mediator of VNS-induced neuroprotection against I/R injury.

Interaction between the hypothalamus and the immune system

NEW FINDINGS

What is the topic of this review? Both branches of the autonomic nervous system are involved in the regulation of the inflammatory response. We explore how the hypothalamus may influence this process. What advances does it highlight? We analyse how a lipopolysaccharide signal is transmitted to the brain and which areas participate in the response of the brain to lipopolysaccharide. Recent studies show that the hypothalamus can influence the inflammatory response by modifying the autonomic output. The biological clock, the suprachiasmatic nucleus, is integrated into this circuit, putting a time stamp on the intensity of the inflammatory response. The brain is responsible for maintaining homeostasis of the organism, constantly adjusting its output via hormones and the autonomic nervous system to reach an optimal setting in every compartment of the body. Also, the immune system is under strong control of the brain. Apart from the conventional systemic responses evoked by the brain during inflammation, such as hypothalamic-pituitary-adrenal axis activation and the induction of sickness behaviour, the autonomic nervous system is now recognized to exert regulatory effects on the inflammatory response. Both branches of the autonomic nervous system are proposed to influence the inflammatory process. Here, we focus on those areas of the brain that might be involved in sensing inflammatory stimuli, followed by how that sensing could change the output of the autonomic nervous system in order to regulate the inflammatory response. Finally, we will discuss how the defenses of the body against a lipopolysaccharide challenge are organized by the hypothalamus.

Electric stimulation of the vagus nerve reduced mouse neuroinflammation induced by lipopolysaccharide

Background

Neuroinflammation (NI) is a key feature in the pathogenesis and progression of infectious and non-infectious neuropathologies, and its amelioration usually improves the patient outcome. Peripheral inflammation may promote NI through microglia and astrocytes activation, an increased expression of inflammatory mediators and vascular permeability that may lead to neurodegeneration. Several anti-inflammatory strategies have been proposed to control peripheral inflammation. Among them, electrical stimulation of the vagus nerve (VNS) recently emerged as an alternative to effectively attenuate peripheral inflammation in a variety of pathological conditions with few side effects.

Considering that NI underlies several neurologic pathologies we explored herein the possibility that electrically VNS can also exert anti-inflammatory effects in the brain.

Methods

NI was experimentally induced by intraperitoneal injection of bacterial lipopolysaccharide (LPS) in C57BL/6 male mice; VNS with constant voltage (5 Hz, 0.75 mA, 2 ms) was applied for 30 s, 48 or 72 h after lipopolysaccharide injection. Twenty four hours later, pro-inflammatory cytokines (IL-1β, IL-6, TNFα) levels were measured by ELISA in brain and spleen extracts and total brain cells were isolated and microglia and macrophage proliferation and activation was assessed by flow cytometry. The level of ionized calcium binding adaptor molecule (Iba-1) and glial fibrillary acidic protein (GFAP) were estimated in whole brain extracts and in histologic slides by Western blot and immunohistochemistry, respectively.

Results

VNS significantly reduced the central levels of pro-inflammatory cytokines and the percentage of microglia (CD11b/CD45^low) and macrophages (CD11b/CD45^high), 24 h after the electrical stimulus in LPS stimulated mice. A significantly reduced level of Iba-1 expression was also observed in whole brain extracts and in the hippocampus, suggesting a reduction in activated microglia.

Conclusions

VNS is a feasible therapeutic tool to attenuate the NI reaction. Considering that NI accompanies different neuropathologies VNS is a relevant alternative to modulate NI, of particular interest for chronic neurological diseases.

Inflammatory Mechanisms Associated with Skeletal Muscle Sequelae after Stroke: Role of Physical Exercise

Inflammatory markers are increased systematically and locally (e.g., skeletal muscle) in stroke patients. Besides being associated with cardiovascular risk factors, proinflammatory cytokines seem to play a key role in muscle atrophy by regulating the pathways involved in this condition. As such, they may cause severe decrease in muscle strength and power, as well as impairment in cardiorespiratory fitness. On the other hand, physical exercise (PE) has been widely suggested as a powerful tool for treating stroke patients, since PE is able to regenerate, even if partially, physical and cognitive functions. However, the mechanisms underlying the beneficial effects of physical exercise in poststroke patients remain poorly understood. Thus, in this study we analyze the candidate mechanisms associated with muscle atrophy in stroke patients, as well as the modulatory effect of inflammation in this condition. Later, we suggest the two strongest anti-inflammatory candidate mechanisms, myokines and the cholinergic anti-inflammatory pathway, which may be activated by physical exercise and may contribute to a decrease in proinflammatory markers of poststroke patients.

Vagus nerve stimulation: state of the art of stimulation and recording strategies to address autonomic function neuromodulation

OBJECTIVE

Neural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.

APPROACH

This review examines the state of the art of VNS applied to two emerging modulations of autonomic function: heart failure and obesity, especially morbid obesity.

MAIN RESULTS

We report that VNS may benefit from improved stimulation delivery using very advanced technologies. However, most of the results from fundamental animal studies still need to be demonstrated in humans.

Chronic Trigeminal Nerve Stimulation Protects Against Seizures, Cognitive Impairments, Hippocampal Apoptosis, and Inflammatory Responses in Epileptic Rats

Trigeminal nerve stimulation (TNS) has recently been demonstrated effective in the treatment of epilepsy and mood disorders. Here, we aim to determine the effects of TNS on epileptogenesis, cognitive function, and the associated hippocampal apoptosis and inflammatory responses. Rats were injected with pilocarpine to produce status epilepticus (SE) and the following chronic epilepsy. After SE induction, TNS treatment was conducted for 4 consecutive weeks. A pilocarpine re-injection was then used to induce a seizure in the epileptic rats. The hippocampal neuronal apoptosis induced by seizure was assessed by TUNEL staining and inflammatory responses by immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). The spontaneous recurrent seizure (SRS) number was counted through video monitoring, and the cognitive function assessed through Morris Water Maze (MWM) test. TNS treatment attenuated the SRS attacks and improved the cognitive impairment in epileptic rats. A pilocarpine re-injection resulted in less hippocampal neuronal apoptosis and reduced level of interleukin-1 beta (IL-1β), tumor necrosis factor-α (TNF-α), and microglial activation in epileptic rats with TNS treatment in comparison to the epileptic rats without TNS treatment. It is concluded that TNS treatment shortly after SE not only protected against the chronic spontaneous seizures but also improved cognitive impairments. These antiepileptic properties of TNS may be related to its attenuating effects on hippocampal apoptosis and pro-inflammatory responses.

Electric stimulation of the ears ameliorated learning and memory impairment in rats with cerebral ischemia-reperfusion injury

Ear acupuncture enhances the secretion of acetylcholine, which has anti-inflammatory effects. Here we want to investigate the effect of electric stimulation (ES) of the ears on learning and memory impairment in rats with cerebral ischemia-reperfusion injury. At 24 h after reperfusion, 2-Hz ES was applied to the ears for 20 min/day (10 min for each ear) for 7 days continuously. The step-through time of the passive avoidance test was greater in the ES group than in the control group (300.0 ± 0.0 s vs 45.0 ± 26.7 s, p < 0.05). Our results showed that neither neurological deficit score nor motor functions were improved after 2-Hz ES (4.0 ± 0 vs 4.5 ± 0.8, p > 0.05). The numbers of nicotinic acetylcholine receptor α4 positively stained cells in the CA2 and dentate gyrus of the hippocampus were 19.0 ± 11.5 and 269.2 ± 79.3, respectively, in the ES group, which were greater than those in the control group (7.0 ± 5.9 and 165.5 ± 30.8, respectively) (both p < 0.05). These results suggested that 2-Hz ES of the ears ameliorated learning and memory impairment in rats with ischemia-reperfusion injury. ES of the ears has neuroprotective effects, which are related to acetylcholine release.

Stimulation of Central α2 Receptors Attenuates Experimental Necrotizing Pancreatitis

OBJECTIVES

Severe necrotizing pancreatitis (SNP) is a disease with relevant morbidity and mortality until today. No specific therapy is in sight. Central α2 agonists such as clonidine and dexmedetomidine are known to have anti-inflammatory effects though the cholinergic anti-inflammatory pathway and are implemented in the clinical routine as adjunct sedative drugs. Their potential effect on SNP has not yet been tested.

METHODS

Severe necrotizing pancreatitis was induced in male Wistar rats. Four treatment groups received either clonidine or dexmedetomidine before (prophylactic) or after induction of SNP (therapeutic). After 12 hours, pancreatic morphologic injury, systemic proinflammatory high-mobility group box 1 protein, and pancreatic and pulmonary myeloperoxidase levels were evaluated.

RESULTS

Severe necrotizing pancreatitis was fully established 12 hours after induction. "Prophylactic" and "therapeutic" administration of clonidine and dexmedetomidine reduced pancreatic morphologic injury (P < 0.05 vs SNP), serum proinflammatory high-mobility group box 1 protein (P < 0.0001 vs SNP), as well as pancreatic and pulmonary myeloperoxidase levels (P < 0.01 vs SNP).

CONCLUSIONS

Prophylactic and therapeutic applications of the central α2 agonists clonidine and dexmedetomidine are effective to attenuate local and systemic injury in experimental SNP and should be evaluated in the clinical setting.

Transcutaneous Cervical Vagus Nerve Stimulation Ameliorates Acute Ischemic Injury in Rats

BACKGROUND

Direct stimulation of the vagus nerve in the neck via surgically implanted electrodes is protective in animal models of stroke. We sought to determine the safety and efficacy of a non-invasive cervical VNS (nVNS) method using surface electrodes applied to the skin overlying the vagus nerve in the neck in a model of middle cerebral artery occlusion (MCAO).

METHODS

nVNS was initiated variable times after MCAO in rats (n = 33). Control animals received sham stimulation (n = 33). Infarct volume and functional outcome were assessed on day 7. Brains were processed by immunohistochemistry for microglial activation and cytokine levels. The ability of nVNS to activate the nucleus tractus solitarius (NTS) was assessed using c-Fos immunohistochemistry.

RESULTS

Infarct volume was 43.15 ± 3.36 percent of the contralateral hemisphere (PCH) in control and 28.75 ± 4.22 PCH in nVNS-treated animals (p < 0.05). The effect of nVNS on infarct size was consistent when stimulation was initiated up to 4 hours after MCAO. There was no difference in heart rate and blood pressure between control and nVNS-treated animals. The number of c-Fos positive cells was 32.4 ± 10.6 and 6.2 ± 6.3 in the ipsilateral NTS (p < 0.05) and 30.4 ± 11.2 and 5.8 ± 4.3 in the contralateral NTS (p < 0.05) in nVNS-treated and control animals, respectively. nVNS reduced the number of Iba-1, CD68, and TNF-α positive cells and increased the number of HMGB1 positive cells.

CONCLUSIONS

nVNS inhibits ischemia-induced immune activation and reduces the extent of tissue injury and functional deficit in rats without causing cardiac or hemodynamic adverse effects when initiated up to 4 hours after MCAO.

Cholinergic anti-inflammatory pathway and gastrointestinal diseases

Upon stimulation, vagus nerves release acetylcholine in local tissues, which can regulate immunecell function and inflammatory responses, operationally through alpha 7 nicotinic acetylcholine receptor. This process is termed cholinergic anti-inflammatory pathway (CAP). It has been shown that CAP exhibits physical functions, and also contributes to the progression of a variety of gastrointestinal diseases, such as inflammatory bowel disease, esophagitis, allergic intestine inflammation, peptic ulcer, colitis, and hepatitis. This review discusses the physical function of CAP, as well as its pivotal role in the development of gastrointestinal diseases.

FoxO proteins in the nervous system

Acute as well as chronic disorders of the nervous system lead to significant morbidity and mortality for millions of individuals globally. Given the ability to govern stem cell proliferation and differentiated cell survival, mammalian forkhead transcription factors of the forkhead box class O (FoxO) are increasingly being identified as potential targets for disorders of the nervous system, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and auditory neuronal disease. FoxO proteins are present throughout the body, but they are selectively expressed in the nervous system and have diverse biological functions. The forkhead O class transcription factors interface with an array of signal transduction pathways that include protein kinase B (Akt), serum- and glucocorticoid-inducible protein kinase (SgK), IκB kinase (IKK), silent mating type information regulation 2 homolog 1 (S. cerevisiae) (SIRT1), growth factors, and Wnt signaling that can determine the activity and integrity of FoxO proteins. Ultimately, there exists a complex interplay between FoxO proteins and their signal transduction pathways that can significantly impact programmed cell death pathways of apoptosis and autophagy as well as the development of clinical strategies for the treatment of neurodegenerative disorders.

miR-210 mediates vagus nerve stimulation-induced antioxidant stress and anti-apoptosis reactions following cerebral ischemia/reperfusion injury in rats

Vagus nerve stimulation (VNS) exerts neuroprotective effects against cerebral ischemia/reperfusion (I/R) injury and modulates redox status, potentially through the activity of miR-210, an important microRNA that is regulated by hypoxia-inducible factor and Akt-dependent pathways. The aim of this study was to determine the mechanisms of VNS- and miR-210-mediated hypoxic tolerance. Male Sprague-Dawley rats were preconditioned with a miR-210 antagomir (A) or with an antagomir control (AC), followed by middle cerebral artery occlusion and VNS treatment. The animals were divided into eight groups: sham I/R, I/R, I/R+AC, I/R+A, sham I/R+VNS, I/R+VNS, I/R+VNS+AC, and I/R+VNS+A. Activation of the endogenous cholinergic a7 nicotinic acetylcholine receptor (a7nAchR) pathway was identified using double immunofluorescence staining. miR-210 expression was measured by PCR. Behavioral outcomes, infarct volume, and neuronal apoptosis were observed at 24 h following reperfusion. Markers of oxidative stress were detected using ELISA. Rats treated with VNS showed increased miR-210 expression as well as decreased apoptosis and antioxidant stress responses compared with the I/R group; these rats also showed increased p-Akt protein expression and significantly decreased levels of cleaved caspase 3 in the ischemic penumbra, as measured by western blot and immunofluorescence analyses, respectively. Strikingly, the beneficial effects of VNS were attenuated following miR-210 knockdown. In conclusion, our results indicate that miR-210 is a potential mediator of VNS-induced neuroprotection against I/R injury. Our study highlights the neuroprotective potential of VNS, which, to date, has been largely unexplored. Since approved by the FDA in 1997, vagus nerve stimulation (VNS) has proven to be a safe and effective treatment for refractory epilepsy and resistant depression. Recent studies have found that VNS also provided neuroprotective effects against ischemic injury in a rat stroke model. We showed that miR-210 played an important role in the antioxidant stress and anti-apoptosis responses induced by VNS. This is the first report showing the effects of VNS at the mRNA level. Therefore, VNS represents a promising candidate treatment for ischemic stroke patients. Schematic view of the role of miR210 mediated in the protective effects of the VNS on the acute cerebral ischemia. VNS acts to activate neuronal and astrocytes a7nAchR , inhibits the apoptosis and oxidant stress responses possibly associated with increased Akt phosphorylation and miR210 expression.

PPARγ upregulation induced by vagus nerve stimulation exerts anti-inflammatory effect in cerebral ischemia/reperfusion rats

Background

It is well known that peroxisome proliferator-activated receptor gamma (PPARγ), a ligand-activated transcription factor, plays a protective role in anti-inflammatory responses in both acute and chronic central nerve system (CNS) insults. Emerging evidence in rats suggests that vagus nerve stimulation (VNS), while restraining inflammatory cytokine production in the peripheral nervous system, also exerts a significant CNS neuroprotective function against ischemic stroke injury. The aim of this study was to explore the role of PPARγ in VNS-mediated anti-inflammatory protection against ischemic stroke damage.

Material/Methods

Adult male Sprague-Dawley rats (total n=160) preconditioned through transfection with either PPARγ small interfering RNA (siRNA) or lentiviral vector without siRNA and surgically subjected to middle cerebral artery occlusion and reperfusion subsequently received VNS treatment at 30 min post-occlusion. The expression of PPARγ after VNS treatment was measured by real-time PCR and Western blotting, also supported by immunofluorescence staining. Subsequently, the neurological deficits scores, the infarct volume, and the brain histopathology were all evaluated. Additionally, the influence on the pro-inflammatory cytokines expression and neuro-immune cells activation was determined by ELISA and immunofluorescence staining.

Results

We found that VNS upregulated expression of PPARγ in ischemia penumbra, diminished the extent of ischemic infarct, alleviated neuronal injury, and suppressed pro-inflammatory cytokine expression and immune cell activation (P<0.05). However, rats with PPARγ silencing failed to manifest significant neuroprotection and anti-inflammatory effect induced by VNS treatment (p>0.05).

Conclusions

PPARγ may participate in the process by which VNS modulates the neuro-inflammatory response following ischemia/reperfusion in rats.